The present invention relates to sensors of the type used in the process control industry. In particular, the present invention relates to a process control temperature sensor.
The temperature of a process fluid is typically measured by a temperature sensor positioned in the fluid. Such temperature sensors typically include an electrical element, such as a thermocouple or RTD, that has an electrical characteristic indicative of the temperature.
To prevent direct contact between the sensitive electrical elements of the sensor and the high temperature environments where the sensor is used, the sensor is often mounted in a protective ceramic tube. Although such ceramic tubes prevent high temperature molten metal or liquids from attacking the thermocouple, they allow corrosive gases to enter the inside of the ceramic tube where the thermocouple is positioned. These gases tend to attack and etch away the metals of the sensor, especially platinum, which is used in thermocouples.